The present invention relates generally to a voltage amplifying circuit, and more particularly to a voltage amplifying circuit that may be capable of having a selectable gain among a plurality of gain values.
Referring to FIG. 7, a circuit schematic diagram of a conventional voltage amplifying circuit is set forth and given the general reference character 700.
Conventional voltage amplifying circuit 700 has a signal input terminal 106, gain changing terminal 108, and a clamp pulse input terminal 109. Conventional voltage amplifying circuit 700 also has a signal output terminal 103.
Conventional voltage amplifying circuit 700 includes power supplies (101a and 101b), voltage amplifiers (102a and 102b), voltage clamp switches (104a and 104b), clamp voltage sources (105a and 105b), inverters (110 to 112), gain changing switches (113 and 114), and capacitors (C101 to C103).
Voltage amplifier 102a includes n-type MOS (metal-oxide-semiconductor) transistors (120a and 121a). Voltage amplifier 102b includes n-type MOS transistors (120b and 121b). Voltage amplifiers (102a and 102b) have identical gains.
Gain changing switches (113 and 114) are n-type MOS transistors.
Because a capacitor C102 is disposed between a gate of n-type MOS transistor 120a and ground, a gain of a signal from signal input terminal 106 to a signal output terminal 103 through voltage amplifier 102a is smaller than the gain of a signal from signal input terminal 106 to signal output terminal 103 through voltage amplifier 102b. 
When a high voltage (such as 5 volts) is applied to gain changing terminal 108, gain changing switch 113 turns off and gain changing switch 114 turns on. Thus, a voltage gain path from signal input terminal 106 to signal output terminal 103 through voltage amplifier 102b is selected and the gain of conventional voltage amplify circuit 700 becomes high. When a low voltage (such as 0 volts) is applied to gain changing terminal 108, gain changing switch 114 turns off and gain changing switch 113 turns on. Thus, a voltage gain path from signal input terminal 106 to signal output terminal 103 through voltage amplifier 102a is selected and the gain of conventional voltage amplify circuit 700 becomes low. In this way, the gain of conventional voltage amplifying circuit 700 can be selected or changed over.
Referring now to FIG. 8, a circuit schematic diagram of a conventional voltage amplifying circuit is set forth and given the general reference character 800.
Conventional voltage amplifying circuit 800 has a signal input terminal 206, gain changing terminal 208, and a clamp pulse input terminal 209. Conventional voltage amplifying circuit 800 also has a signal output terminal 203.
Conventional voltage amplifying circuit 800 includes power supplies (201a and 201b), voltage amplifiers (202a and 202b), voltage clamp switches (204a and 204b), clamp voltage sources (205a and 205b), inverters (210 to 212), gain changing switches (213 and 214), and capacitors (C201 and C202).
Voltage amplifier 202a includes n-type MOS transistors (220a and 221a). Voltage amplifier 202b includes n-type MOS transistors (220b and 221b). Voltage amplifier 202a has a gain that is larger than voltage amplifier 202b. FIG. 9 is a graph illustrating voltage transfer characteristics of voltage amplifiers (202a and 202b). The gain can be ascertained by the slope of the transfer characteristics. As illustrated in FIG. 9, voltage amplifier 202a has a higher gain than voltage amplifier 202b. 
Referring once again to FIG. 8, when a high voltage (such as 5 volts) is applied to gain changing terminal 208, gain changing switch 213 turns off and gain changing switch 214 turns on. Thus, a voltage gain path from signal input terminal 206 to signal output terminal 203 through voltage amplifier 202b is selected and the gain of conventional voltage amplify circuit 800 becomes low. When a low voltage (such as 0 volts) is applied to gain changing terminal 208, gain changing switch 214 turns off and gain changing switch 213 turns on. Thus, a voltage gain path from signal input terminal 206 to signal output terminal 203 through voltage amplifier 202a is selected and the gain of conventional voltage amplify circuit 800 becomes high. In this way, the gain of conventional voltage amplifying circuit 800 can be selected or changed over.
Referring now to FIG. 10, a circuit schematic diagram of yet another conventional voltage amplifying circuit is set forth and given the general reference character 1000.
Conventional voltage amplifying circuit 1000 has a signal input terminal 306, gain changing terminal 308, and a clamp pulse input terminal 309. Conventional voltage amplifying circuit 1000 also has a signal output terminal 303.
Conventional voltage amplifying circuit 1000 includes a power supply 301, a voltage amplifier 302, a voltage clamp switch 304, a clamp voltage source 305, inverters (310 and 311), and a capacitor C301.
Voltage amplifier 302 includes n-type MOS transistors (320 to 322).
In voltage amplifier 302, n-type MOS transistors (320 and 321) are used as resistors or loads. N-type MOS transistor 321 is turned on or off to select or change over the gain.
When a high voltage (such as 5 volts) is applied to gain changing terminal 308, n-type MOS transistor 321 turns off. Thus, the gain of conventional voltage amplify circuit 1000 becomes low. When a low voltage (such as 0 volts) is applied to gain changing terminal 308, n-type MOS transistor 321 turns on. Thus, the gain of conventional voltage amplify circuit 1000 becomes high. In this way, the gain of conventional voltage amplifying circuit 1000 can be selected or changed over.
In conventional voltage amplifying circuit 700 of FIG. 7, even the operating speed may not change for the two selectable gains because both voltage amplifiers (102a and 102b) have the same gain. However, in conventional voltage amplifying circuit 800 of FIG. 8, the operating speed can differ when the gain is changed over because voltage amplifiers (202a and 202b) have different gains. In conventional amplifying circuits (700 and 800), the circuit size can be relative large because two voltage amplifiers are used. Also, because two voltage amplifiers are used and enabled at all times (an output from one of the two voltage amplifiers is selected), power consumption is relatively large.
On the contrary, conventional voltage amplifying circuit 1000 uses only one voltage amplifier. Thus, the circuit area and power consumption may be reduced as compared with conventional voltage amplifying circuits (700 and 800). However, in conventional voltage amplifying circuit 1000, the amount of current flowing in voltage amplifier 302 varies in accordance with whether n-type MOS transistor 321 is on or off. The change in current causes change in operating speeds and power consumption. The operating speed and power consumption changes more as the gain variation ratio (ratio of the high gain to the low gain) becomes larger. Therefore, conventional voltage amplifying circuit 1000 may be effective for a case where there is a small gain and a gain variation ratio is only about two. However, for large gains and large gain ratios, the power consumption may be large and the operation speed differences may be relatively large.
In view of the above discussion, it would be desirable to provide a voltage amplifying circuit, which may have a reduced circuit area and/or power consumption. It would also be desirable to provide a voltage amplifying circuit in which operating speed variation and/or power consumption variation is suppressed when a gain is changed over or switched.
According to the present embodiments, a voltage amplifying circuit may have a selectable gain. A voltage amplifying circuit may include a voltage amplifier and a gain changing unit. A gain changing unit may be capable of changing at least one of: a capacitance between a signal input terminal and an input terminal of a voltage amplifier and a capacitance between an input terminal of a voltage amplifier and a ground or a first reference potential. In this way, a gain from a signal input terminal to an output terminal of a voltage amplifying circuit may be changed.
According to one aspect of the embodiments, a voltage amplifier may amplify an input signal received at a voltage amplifier input terminal and provide an output signal at a voltage amplifier output terminal.
According to another aspect of the embodiments, the gain changing circuit may include a first capacitor, a second capacitor, a first switch, and a second switch. The first capacitor may have a first terminal connected to a signal input terminal and a second terminal connected to a voltage amplifier input terminal. The second capacitor may have a first terminal connected to a voltage amplifier input terminal. The first switch may be coupled between a second terminal of the second capacitor and a first reference potential. The second switch may be connected between the signal input terminal and the second terminal of the second capacitor.
According to another aspect of the embodiments, the gain changing circuit may include a first capacitor, a second capacitor, a third capacitor, a first switch, a second switch, a third switch, and a fourth switch. The first capacitor may have a first terminal connected to a signal input terminal and a second terminal connected to a voltage amplifier input terminal. The second capacitor may have a first terminal connected to a voltage amplifier input terminal. The third capacitor may have a first terminal connected to the voltage amplifier input terminal. The first switch may be coupled between a second terminal of the second capacitor and a first reference potential. The second switch may be connected between the signal input terminal and the second terminal of the second capacitor. The third switch may be coupled between the signal input terminal and a second terminal of the third capacitor. The fourth switch may be coupled between the second terminal of the third capacitor and the first reference potential.
According to another aspect of the embodiments, a gain circuit may include a first capacitor, a second capacitor, a first switch, and a second switch. The first capacitor may have a first terminal connected to a signal input terminal and a second terminal connected to a voltage amplifier input terminal. The second capacitor may have a first terminal connected to a voltage amplifier input terminal. The first switch may be coupled between a second terminal of the second capacitor and a voltage amplifier output terminal. The second switch may be connected between the signal input terminal and the second terminal of the second capacitor.
According to another aspect of the embodiments, a voltage amplifier circuit may include a voltage clamp circuit. The voltage clamp circuit may provide an operating voltage to a voltage amplifier input terminal in response to a clamp signal.
According to another aspect of the embodiments, a voltage amplifier may include a first transistor and a load device. A first transistor may have a controllable impedance path disposed between a first reference potential and a voltage amplifier output terminal and may have a control terminal connected to a voltage amplifier input terminal. A load device may be disposed between a second reference potential and a voltage amplifier output terminal.
According to another aspect of the embodiments, a voltage amplifier circuit may have a gain that can be selectable among a plurality of gain values. A voltage amplifier circuit may include a voltage amplifier and a gain changing unit. A voltage amplifier may receive a voltage amplifier input signal at a voltage amplifier input terminal and may provide an amplified signal at a voltage amplifier output terminal. A gain changing unit may receive a signal input at a signal input terminal and a first gain changing signal at a first gain changing terminal and may provide a voltage amplifier input signal. The gain of the voltage amplifier circuit may be selectable by changing the value of a capacitance between the signal input terminal and the voltage amplifier input terminal.
According to another aspect of the embodiments, a gain changing unit may include a first capacitor, a second capacitor, a first switch, and a second switch. A first capacitor may have a first terminal connected to the signal input terminal and a second terminal connected to the voltage amplifier input terminal. A second capacitor may have a second terminal connected to the voltage amplifier input terminal. The first switch may be disposed between the signal input terminal and a first terminal of the second capacitor. The first switch may have a first switch high impedance state when the first gain changing signal is in a first low gain state. The first switch may have a first switch low impedance state when the first gain changing signal is in a first high gain state. The second switch may be disposed between a first potential and the first terminal of the second capacitor. The second switch may have a second switch low impedance state when the first gain changing signal is in a first low gain state. The second switch may have a second switch high impedance state when the first gain changing signal is in a first high gain state.
According to another aspect of the embodiments, a gain changing circuit may include a third capacitor, a third switch, and a fourth switch. The third capacitor may have a second terminal connected to the voltage amplifier input terminal. The third switch may be disposed between the signal input terminal and a first terminal of the third capacitor. The third switch may have a third switch high impedance state when a second gain changing signal is in a second low gain state. The third switch may have a third switch low impedance state when the second gain changing signal is in a second high gain state. The fourth switch may be disposed between a first potential and the first terminal of the third capacitor. The fourth switch may have a fourth switch low impedance state when the second gain changing signal is in a second low gain state. The fourth switch may have a fourth switch high impedance state when the second gain changing signal is in a second high gain state.
According to another aspect of the embodiments, the gain may be selectable among at least four gain values.
According to another aspect of the embodiments, a gain changing unit includes a first capacitor, a second capacitor, a first switch, and a second switch. The first capacitor may have a first terminal connected to the signal input terminal and a second terminal connected to the voltage amplifier input terminal. The second capacitor may have a second terminal connected to the voltage amplifier input terminal. The first switch may be disposed between the signal input terminal and a first terminal of the second capacitor. The first switch may have a first switch high impedance state when the first gain changing signal is in a first low gain state and a first switch low impedance state when the first gain changing signal is in a first high gain state. A second switch may be disposed between the voltage amplifier output terminal and the first terminal of the second capacitor. The second switch may have a second switch low impedance state when the first gain changing signal is in the first low gain state and a second switch high impedance state when the first gain changing signal is in the first high gain state.
According to another aspect of the embodiments, a voltage amplifier circuit may have a gain that can be selectable among a plurality of gain values. A voltage amplifier circuit may include a voltage amplifier and a gain changing unit. A voltage amplifier may receive a voltage amplifier input signal at a voltage amplifier input terminal and may provide an amplified signal at a voltage amplifier output terminal. A gain changing unit may receive a signal input at a signal input terminal and a first gain changing signal at a first gain changing terminal and may provide a voltage amplifier input signal. The gain of the voltage amplifier circuit may be selectable by changing the value of a capacitance between the signal input terminal and the voltage amplifier input terminal in response to the first gain changing signal.
According to another aspect of the embodiments, a gain changing unit may include a first capacitor, a second capacitor, a first insulated gate field effect transistor (IGFET), and a second IGFET. A first capacitor may have a first terminal connected to the signal input terminal and a second terminal connected to the voltage amplifier input terminal. A second capacitor may have a second terminal connected to the voltage amplifier input terminal. The first IGFET may be disposed between the signal input terminal and a first terminal of the second capacitor. The first IGFET may have a first IGFET high impedance state when the first gain changing signal is in a first low gain state. The first IGFET may have a first IGFET low impedance state when the first gain changing signal is in a first high gain state. The second IGFET may be disposed between a first potential and the first terminal of the second capacitor. The second IGFET may have a second IGFET low impedance state when the first gain changing signal is in a first low gain state. The second switch may have a second switch high impedance state when the first gain changing signal is in a first high gain state.
According to another aspect of the embodiments, a gain changing circuit may include a third capacitor, a third IGFET, and a fourth IGFET. The third capacitor may have a second terminal connected to the voltage amplifier input terminal. The third IGFET may be disposed between the signal input terminal and a first terminal of the third capacitor. The third IGFET may have a third IGFET high impedance state when a second gain changing signal is in a second low gain state. The third IGFET may have a third IGFET low impedance state when the second gain changing signal is in a second high gain state. The fourth IGFET may be disposed between a first potential and the first terminal of the third capacitor. The fourth IGFET may have a fourth IGFET low impedance state when the second gain changing signal is in a second low gain state. The fourth IGFET may have a fourth IGFET high impedance state when the second gain changing signal is in a second high gain state.
According to another aspect of the embodiments, the gain may be selectable among at least four gain values.
According to another aspect of the embodiments, a gain changing unit includes a first capacitor, a second capacitor, a first IGFET, and a second IGFET. The first capacitor may have a first terminal connected to the signal input terminal and a second terminal connected to the voltage amplifier input terminal. The second capacitor may have a second terminal connected to the voltage amplifier input terminal. The first IGFET may be disposed between the signal input terminal and a first terminal of the second capacitor. The first IGFET may have a first IGFET high impedance state when the first gain changing signal is in a first low gain state and a first IGFET low impedance state when the first gain changing signal is in a first high gain state. A second IGFET may be disposed between the voltage amplifier output terminal and the first terminal of the second capacitor. The second IGFET may have a second IGFET low impedance state when the first gain changing signal is in the first low gain state and a second IGFET high impedance state when the first gain changing signal is in the first high gain state.
According to another aspect of the embodiments, the voltage amplifier circuit may further include a voltage clamp IGFET having a voltage clamp impedance path disposed between a clamp potential and the voltage amplifier input terminal and a voltage clamp IGFET control terminal receiving a voltage clamp signal.
According to another aspect of the embodiments, a voltage amplifier may include an amplifying IGFET and a load IGFET. An amplifying IGFET may have a controllable impedance path disposed between a first potential and a voltage amplifier output terminal and may have a control terminal connected to a voltage amplifier input terminal. A load IGFET may be disposed between a second potential and a voltage amplifier output terminal.